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Resumen

Nowadays there is no dominant technology for the concentrated solar power plants that means there is still a way to go. Within this context, new concepts for solar fields and power cycles are being studied. One of them is the proposed on this paper: the integration of line-focusing solar field, with parabolic trough or linear Fresnel solar collectors, with molten salts as heat transfer fluid and supercritical carbon dioxide Joule-Brayton power cycles. This concept works as a feasible design solution to increase efficiency and reduce final energy cost in solar electricity production. In this work, four Joule-Brayton cycles configurations were assessed and compared with the considered reference, a concentrated solar power plant with direct steam generation in the solar field and a Rankine power cycle. The studied Joule-Brayton cycles are: simple cycle, recompression cycle, partial cooling with recompression cycle and recompression with main compression intercooling cycle. The common operation conditions for all the configurations are that at design-point the high pressure turbine inlet temperature value is 550ºC, this limit was established considering maximum temperature allowed by selective coating material in linear receivers. Also is analyzed the hypothetical scenario of increasing the turbine inlet temperature to 650ºC, extrapolating the receivers heat losses regressions. The innovative configurations of solar field and supercritical carbon dioxide power cycles increase plant efficiency, for recompression cycle configuration, up to 46.84% (550ºC turbine inlet) and 50.85% (650ºC turbine inlet), and reduces required solar field effective aperture area and land area for a fixed plant power output. Proposed configurations, parabolic trough collector and linear Fresnel coupled with a Joule-Brayton cycle decreases the solar field required for the same net power. Relating to power block, the supercritical carbon dioxide higher density in comparison with water steam, reduces turbines and compressors dimensions, footprint and final cost, but is a technology nowadays under industrial development and final turbo machines cost could not be assessed in this study. Another important keystone in JouleBrayton cycle costs are the heavy duty heat exchangers required. Printed circuit heat exchangers are the most advisable solution proposed for supercritical carbon dioxide recuperators, mainly due to higher compactness and better heat transfer coefficient inside channels. However, in this paper it is demonstrated how common shell & tube heat exchangers, with AISI 347 (austenitic) stainless steels, are competitive and feasible solutions for the primary and reheating molten salts – carbon dioxide heat exchangers.